The usefulness of the phenomenon of magnetostrictivity in linear distance or position measuring devices is recognized by the prior art; for example, see Krisst U.S. Pat. Nos. 4,071,818; Chamuel 4,144,559; Ueda et al. 4,238,844; Bailey et al., 3,423,673 and Tellerman 3,898,555. Common to several devices are a magnetostrictive wire which runs in a straight line path through the measurement field, means for inducing a torsional strain at a given position along the wire, and a magnet which is displaceable along the wire, either by connection to a movable body such as a machine tool or by reason of association with a float device. Generally speaking, the position of the magnet represents the position of the monitored quantity and is determined as a function of the time required for a torsional disturbance to propagate from one end of the wire through the area of influence of the magnet.
At least two problems have been encountered by prior art devices of the class described immediately above. The first arises out of the physical make-up of the components by which the torsional disturbance is created; i.e., these devices typically require a welded connection between the wire and the actuator and are fragile in nature and easily broken. The other problem arises out of the fact that the arrival of the torsional disturbance at the location of influence of the magnet creates a voltage having the characteristic of a damped sinewave and it is common to sense the sinewave at the point of amplitude coincidence with a "trip voltage." However the time required for the induced voltage to rise to the trip voltage can vary with a number of factors including temperature and the intensity of the torsional disturbance. Therefore, the sense point may vary considerably in time and this variance may have a considerable effect on the accuracy of a measurement device and the suitability of the measurement device to applications having a very high accuracy and resolution requirement.